PROJECT SUMMARY Actinic neoplasia (precancerous actinic keratosis and non-melanoma skin cancer) is the most common type of human neoplasia, and the most common diagnosis in VA dermatology clinics. We and other groups have characterized the mechanisms by which aging and ultraviolet B radiation (UVB) contribute to actinic neoplasia. In particular, human skin at high risk for actinic neoplasia exhibits biochemical features, including decreased keratinocyte expression of DNA repair enzymes, increased numbers of senescent fibroblasts with lower levels of fibroblast IGF-1, and increased fibroblast cytokines including IL-6, IL-8 and TNF. Moreover, at risk skin responds to UVB by generating basal keratinocytes proliferating while still harboring DNA mutations. This revised VA Merit application will leverage our recent findings that a noninvasive, multi-spectral, mesoscopic imaging platform could potentially identify clinically normal-appearing skin at risk for actinic neoplasia. This proposal also provides evidence that mesoscopic imaging could have use in quantifying field carcinogenesis. To that end, two specific aims will test the hypothesis that mesoscopic imaging will be able to discern skin with biochemical and functional characteristics of tissue at high risk for actinic neoplasia. The first aim consists of two parts. In the first part, mesoscopic imaging will be used to predict areas of at-risk vs. normal skin, which will be tested with biopsies and non-invasive transcriptome analysis to compare imaging parameter-based predictions against biochemical, histological and functional features associated with skin at high risk for actinic neoplasia. In the second part of Aim 1 we will take advantage of our recent findings that wounding of photo- damaged geriatric skin with fractionated laser resurfacing normalizes the actinic neoplastic biochemical/histological changes. We will leverage these findings by conducting mesoscopic imaging of laser- wounded vs unwounded skin in geriatric subjects with photo-damaged skin. The second aim will test the ability of mesoscopic imaging to quantify the effectiveness of topical photodynamic therapy (PDT) performed or chemotherapy agent 5-fluorouracil cream on subjects with multiple actinic keratosis requiring field therapy. Additionally, subjects at high risk for actinic neoplasia not treated with field therapy will be monitored longitudinally in clinics by serial mesoscopic imaging. These three strategies in Aim 2 will test if this noninvasive imaging can predict where actinic keratosis will arise and assess if mesoscopic imaging has use in the clinic for quantifying skin at-risk for actinic neoplasia and actinic keratosis. The overall goal is to establish a fast, wide- field, multi-spectral imaging system that can provide quantitative imaging parameters for monitoring human skin non-invasively. If successful, these studies will validate a valuable clinical tool that can stratify risk of actinic neoplasia even when skin appears clinically normal. Moreover, this non-invasive, image-based contrast mapping approach could serve to propel research in field cancerization using skin as a model system, which could be adapted to other organ systems such as colon, esophagus and lung cancers. These studies will improve the care of veterans served in our dermatology clinics. This proposal will also provide valuable tools for both the study and monitoring of many cancer types found in US Veterans.